1. Field of the Invention
This invention relates to maintaining the densities of inks put down on a paper web as same is being fed from a multi-color printing press.
2. Description of the Prior Art
In a typical printing press, multi-colored data is printed repetitively on a web of paper fed from the press using a plurality of zone controlled inking units. The number of inking units corresponds to the number of different colors that may be applied to the web while the number of zones in a unit corresponds to the number of patches of ink that can be put down by a given inking unit.
The density of each patch is dependent on the amount of ink deposited on the paper during printing. Ordinarily, the amount to be deposited is preset prior to the commencement of a run.
From a quality standpoint, proper color density must be established and maintained throughout the run. In the past, there have been systems to monitor the quality of the print and correct it when there is a variation from a preset standard. This is accomplished by adjustment of the inking elements to change the amount of ink being deposited.
Prior art teaches some methods to detect the density of the ink laid down on the paper by evaluating a color bar with some type of detector means. Variations in density are noted and ink adjustments are made to correct for the variation. Examples of same are found in: Schramm, et al., U.S. Pat. No. 4,200,932; Lecha, U.S. Pat. No. 4,752,892; Brunner, U.S. Pat. No. 4,852,485; Keller, et al., U.S. Pat. No. 4,975,862; Pfeiffer, U.S. Pat. No. 5,122,977; Kipphan, et al., U.S. Pat. No. 5,182,721; and, Christie, Jr., et al., U.S. Pat. No. 4,003,660.
It is also known that video inspection is an important part of some process controls. A key element of the inspection of a high speed object, such as a printed web, is the synchronization of a stroboscopic light source and video source. This is done in such a way as to stop the action of motion with the area or object of interest in the field of view of the video source. An example of same is found in Gneuchtel, et al., U.S. Pat. No. 4,794,453.